The present invention relates to a centralizer for use in wellbore operations. More specifically, the present invention relates to a centralizer with compressible bow springs, particularly a stabilizer that is used in relatively small annular spaces and which also expands for use in a larger annular space. In another aspect, the present invention relates to a centralizer that provides a minimum standoff and/or centralization in portions of a wellbore in which known bow spring centralizers cannot provide adequate standoff because the bow springs lack sufficient restoring force.
Bow spring centralizers are used to center one tubular member inside a borehole or other tubular member, e.g., to center a first smaller tubular member in a second, larger diameter, tubular member (for instance, a tubing string inside a casing in a borehole). Typically, centralizers are run into the borehole on the exterior of an inner tubular member or tubing string and the bow springs project radially outwardly from the outside diameter (O.D.), or surface, of the smaller tubular member into contact with the inside diameter (I.D.), or surface, of the larger diameter tubular. However, there are at least two disadvantages of prior known centralizers in that they tend to restrict fluid flow in the annular space between centralizer O.D. and the I.D. of the tubular member and, in the event the smaller diameter tubular member needs to be rotated inside the larger diameter tubular member (if, for instance, it becomes stuck during running), rotating tends to damage the bow springs of such centralizers.
Another disadvantage of many known centralizers is illustrated by reference to the many wells that include a portion that is cased and a portion that is not cased, wells in which the diameter of the bore changes, or wells that include one or more lateral bores. Downhole operations must, of course, be conducted in cased, uncased, different diameter, and/or lateral bores. In such wellbores, the centralizer must pass through a portion of the bore that is relatively small and then down through a portion that is smaller, with the centralizing function needed in the larger diameter, deeper portion of the wellbore. So far as is known, no centralizer is available that is capable of both being run into such bores and then also providing effective centralizing in a larger diameter portion of the wellbore. Similarly, no centralizer is known that provides effective centralizing in bores of both diameters.
Another limitation of known centralizers occurs in the curved portion of a wellbore. In such wellbores, the weight of the tubing or pipe to which the centralizer is mounted can exceed the restoring force of the bow springs such that the tubing or pipe bears against the side of the wellbore. This same problem of the weight of the tubing affects lateral bores, restricting fluid flow and preventing the rotation of the tubing string. There is, therefore, a need for, and it is an object of the present invention to provide, a centralizer that positions the tubing or pipe string off the side of the wellbore in the curved or the horizontal portion of a wellbore and a centralizer that allows rotation of the tubing string in the wellbore.
Another limitation of known centralizers occurs when the wellbore, or a portion of the wellbore, wellhead, or flow control equipment is of relatively small diameter. When introduced into such restrictions, the bow springs of known centralizers must be highly compressed, creating substantial resistance to entry of the centralizer into the wellbore and/or the running of the centralizer in the wellbore. Further, because of the increased tendency of the bow springs to return to their uncompressed state as a result of their high compression, the likelihood that the centralizer will catch and hang up in the wellbore, wellhead, or flow control equipment is increased. The high compression that is required in such restrictions in the wellbore is sometimes even enough to overcome the restoring force of the bow springs such that the bow springs are unable to return to their uncompressed state. There is, therefore, a need for a centralizer that provides effective centralizing in a wellbore that is capable of being run into even small diameter wellbores and/or restrictions in the wellbore, and it is an object of the present invention to provide a centralizer that functions effectively even when run through such restrictions in the wellbore.
It is also an object of the present invention to provide positive centralization in areas of the wellbore where a bow spring is not strong enough to position the pipe or tubing string off the side of the well bore but also provide standoff in less severe portions of the borehole.
Another object of the present invention is to provide a centralizer that functions in both a large and/or small diameter annulus and/or wellbore.
Another object of the present invention is to provide a centralizer that maintains both standoff from the wall of the borehole and fluid flow through the borehole.
Yet another object of the present invention is to provide a centralizer that can be run into a borehole through a borehole of small diameter, e.g., a cased portion of the borehole, that also functions to center the tubing in a portion of the borehole having a diameter larger than the small diameter portion such as an uncased portion of the borehole.
Other objects, and the advantages, of the present invention will be made clear to those skilled in the art by the following description of a presently preferred embodiment thereof.